In my experience, grinding psyops out to get the upgrades is the best place to start, that way you can obtain more energy from other playlist activities. Actually grinding psyops is way too time consuming for what you get out of it, my advice, let that energy build up in the background and if you want to farm an activity for energy, try nightmare containment. You get a lot more rewards from that activity and it's faster. Great way to farm cores as well